I recommend visiting - Koh Tao, Thailand
Halong Bay in Vietnam is a truly amazing location and a must for any itinerary to Vietnam. The overnight junks that you stay on are beautifully decorated and waking up to the scenery in Halong Bay is a really memorable. The food onboard the junks is fantastic, and kayaking through the lagoons with virtually no one else in sight is really an unforgettable experience. The photo opportunities are pretty amazing too!